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1. Neurons are electrically active;
They have a resting voltage, and can
undergo electrical changes
2. Neurons can “fire”; They
generate Action Potentials
that move along the axon
3. When the action potential
reaches the terminals, it causes a
chemical signal (neurotransmitter)
to be released, which moves
across the synapse to affect a
second neuron.
Fig. 1.6.1
Membrane Proteins and the Movement of Ions
Na+ pump
(Na+/K+ pump)
Actively pumps Na+
out of cell
Na+ Na+
Na+
Receptor
enzyme
Fig. 1.6.2
Second
Messenger
production
Chloride channels are open
K+
K+
EPSP, IPSP AND ACTION
POTENTIAL
60
VOLTAGE (mV)
40
ACTION
POTENTIAL
20
0
Larger
EPSP
-20
-40
EPSP
threshold
Resting
Membrane
Potential
-60
-80
IPSP
-100
0
10
20
30
40
TIME ----->
Fig. 1.6.3
50
60
70
TRANSMITTER BINDING TO A RECEPTOR
inside
RECEPTOR
Chemically Gated
Channel Opens:
Ions Move
Into Cell
(can be EPSP or
IPSP depending
on the channel
membrane
Fig. 1.6.4
outside
WHEN THE TRANSMITTER AND
RECEPTOR ARE BOUND TO
EACH OTHER, IT STIMULATES
BIOLOGICAL ACTIVITY
NEUROTRANSMITTER
Action Potential is Generated
K+
K+
Na+
Na+ moves inVoltage moves more positive
(ascending limb)
Na+ Na+
Na+
K+ moves outrestores resting
Potential (i.e.,
descending limb)
Towards
soma
Fig. 1.6.5
AXON
Towards
terminals
INFORMATION PROCESSING BY
NEURONS
Each neuron is like a
tiny computer; it
receives many
inputs, both
excitatory and
inhibitory, and adds
them together (i.e.
summation) over
time and space.
If the summed excitatory
input at the initial part of the
axon exceeds the threshold,
an action potential is fired.
Fig. 1.6.6
INFORMATION PROCESSING BY
NEURONS: THE ACTION POTENTIAL
LOW FREQUENCY
LIGHT
OFF
HIGH FREQUENCY
LIGHT
ON
VISUAL SYSTEM NEURON
Fig. 1.6.7
Chemical Transmission
Synthesis
Storage
Release
Calcium flowing into the
terminal, which is caused
by the action potential,
stimulates transmitter
release.
Fig. 1.6.8
Postsynaptic Action (a) and Inactivation (b, c)
Fig. 1.6.9